Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Detail) - Financial Standby Letter of Credit $ in Millions	Mar. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Commitments	$ 2,945
Less Than One Year From The Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,673	[1]
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,244	[1]
More than five years from balance sheet date
Line of Credit Facility [Line Items]
Commitments	$ 28

[1] Includes $25 and $15 issued on behalf of commercial customers to facilitate trade payments in U.S. dollars and foreign currencies which expire less than 1 year and between 1 - 5 years, respectively.